Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-08-07
2001-10-09
Bost, Dwayne (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S012100, C455S013200
Reexamination Certificate
active
06301476
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to satellite communications systems and, in particular, to satellite communications systems that are operable with hand-held user terminals for providing communication links to existing telephone and/or network infrastructures.
BACKGROUND OF THE INVENTION
Satellite telephone systems are emerging as a new and important global business. These systems utilize many individual circuits routed through one satellite or a constellation of many satellites to provide communications for terrestrial terminals. One significant advantage of the satellite telephone system is that it provides ubiquitous coverage of large areas of the earth without requiring the construction of many small terrestrial cells.
In the past, satellites have employed antennas that produce antenna beams to provide coverage to areas occupied by users or subscribers. For full duplex communication systems, it has been the practice for the beam pattern of the region covered by the antenna for transmission to be identical to the beam pattern of the region covered by the antenna for reception; i.e., the beam pattern of the regions for transmission is congruent with the beam pattern of the region covered for reception.
It has also been the practice to fill desired satellite service regions with more than one beam when there has been insufficient allocated bandwidth (frequency range) to serve a required number of users with a required bandwidth, and to lower the power requirements of both the satellites and the earth stations. This approach relies on the re-use of the allocated bandwidth with spatial diversity. Spatial diversity is established by dividing the service region into sub-regions, and employing separate and unique smaller beams or sub-beams to serve each service sub-region. This technique enables frequency re-use through spatial diversity, wherein adjacent sub-beams operate at different frequencies, and wherein non-adjacent sub-beams may use the same frequency, thereby avoiding interference between the users located in the non-adjacent sub-beams.
In the past, the transmission sub-regions (or sub-beams) have been defined to be the same shape and size as the corresponding reception sub-regions (or sub-beams). This is typically done in order to simplify signal routing and the overall system architecture.
FIG. 1
depicts an example of a multibeam antenna beam pattern that can be used for both reception by user terminals (downlink) and transmission from user terminals (uplink). That is, the downlink beam pattern and the uplink beam pattern are substantially identical, or congruent, at the surface of the earth. In
FIG. 1
the service region (SR) is partitioned into
16
sub-regions, individual ones of which are serviced by one sub-beam (assuming no sub-beam overlap). The pattern is characterized by a central sub-beam
1
, a ring of six inner sub-beams (
2
-
7
), and a ring of nine outer sub-beams (
8
-
16
). Phased arrays are one suitable antenna type for generating such beam patterns. Reference in this regard can be had to, by example, U.S. Pat. No. 5,422,647, issued Jun. 6, 1995, entitled “Mobile Communication Satellite Payload”, by E. Hirshfield and C. A. Tsao; U.S. Pat. No. 5,283,587, issued Feb. 1, 1994, entitled “Active Transmit Phased Array Antenna”, by E. Hirshfield; and to U.S. Pat. No. 5,504,493, issued Apr. 2, 1996, entitled “Active Transmit Phased Array Antenna with Amplitude Taper”, by E. Hirshfield.
More particularly, in the past satellites used for duplex communications have (as best as could be designed) congruent antenna beam coverage areas for a given uplink and downlink. For example, if a satellite has a certain coverage area and that coverage area is covered by sixteen separate beams (sub-beams) for the uplink and downlink, the sixteen beam coverage areas for the uplink are the same coverage areas for the downlink (with boundary lines located within, for example, 30 miles of one another), as shown in FIG.
1
.
That is, in the conventional implementations of satellites used for duplex communications, the antenna beam area of the service links was designed to be the same for the uplink and the downlink. This was done for simplicity in satellite antenna design, simplicity in ground operations, and, when using conventional parabolic antennas, the antenna design optimization could be the same for the uplink frequency and the downlink frequency.
The inventors have realized that the use of fixed congruent sub-beams for transmission and reception, as in
FIG. 1
, can in some instances result in inefficiencies and a loss of overall system flexibility.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is a first object and advantage of the invention to provide a satellite communication system having sub-beam patterns that overcome the foregoing and other problems.
It is a further object and advantage of this invention to provide a satellite communication system wherein individual satellites each service a congruent uplink and downlink service region, but wherein the sub-regions (or sub-beams) are non-congruent.
It is a further object of this invention to provide a satellite communication system that employs non-congruent antenna beam coverage areas for the uplink and downlink, with the antenna beam coverage areas being separately optimized for each of the uplink and the downlink without consideration for the antenna beam coverage areas of the other.
It is one further object of this invention to provide a satellite communication system wherein individual satellites each service a congruent uplink and downlink service region, but wherein the sub-regions (or sub-beams) are non-congruent, and wherein the shapes of the sub-regions can be dynamically controlled, either from a ground station or the satellite, as a function of current or expected signal routing constraints, system loading, and other factors.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
The inventors have realized that user terminal service links do not require congruent antenna beam coverage areas because the gateway (in the case of a repeater satellite) or the satellite (in the case of a satellite that performs on-board signal processing) can determine which beam a given user is located in separately for the uplink and the downlink. With the advent of modern antenna designs (e.g., phased arrays, both passive and active), the optimization in antenna gain pattern for the downlink (transmitting) satellite antenna may not lead to the same antenna beam coverage areas as the antenna beam coverage areas that are optimized in antenna gain pattern for the uplink (receiving) satellite antenna. These different antenna beam coverage areas can be accommodated with knowledge of the patterns on the ground in the gateway or in the satellite.
As such, in accordance with this invention a communication satellite has a downlink transmit service antenna and an uplink receive service antenna, wherein the downlink transmit service antenna and the uplink receive service antenna are separately optimized for their intended functions without regard for maintaining congruency, at the ground, of the individual sub-beams or coverage areas of the two antennas.
Also disclosed is a method for use in a satellite communications system of a type that has at least one satellite having forward and reverse beams each comprised of sub-beams for relaying user communications between a ground station and user terminals. The method optimizes signal flow between the ground station and the user terminals and includes the steps of: (a) determining user terminal RF signal conditions within the sub-beams of at least one of the forward and reverse beams; and (b) in response to the determined RF signal conditions, re-allocating sub-beams of at least one of the forward and reverse beams such that the totality of the sub-beams of the forward beam are non-congruent with the totality of the sub-beams of the r
Hirshfield Edward
Monte Paul A
Bost Dwayne
Gelin Jean A
Globalstar L.P.
Ohlandt Greeley Ruggiero & Perle L.L.P.
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